The present invention relates to a thermophotovoltaic converter of the type comprising a concentrating optical system and a chamber formed by a transducer of solar radiation comprising a lens and at least one photovoltaic cell.
It is known that the sun emits energy in the form of electromagnetic radiation, the wavelengths of which lie essentially between 0.2 and 3 .mu.m. However, silicon photovoltaic cells exhibit a high degree of efficiency substantially in the spectral range between 0.6 and 1 .mu.m, with a maximum in the region of 0.85 .mu.m, outside which these cells become hot and are subject to a rapid loss of efficiency.
The converters in common use are of the filter type or of the type based on a thermal principle, using in both cases an optical focusing unit.
The converters of the type with filters essentially comprise at least one filter which selects and conveys the solar radiation, the wavelengths of which lie substantially within a range of between 0.6 and 1 .mu.m, to a silicon photovoltaic cell. The rejected radiation, which is not conveyed by said filter, is often used to strike a photovoltaic cell sensitive thereto, for example of germanium type, directly or via a subsequent filter which, in this case, selects the radiation of a wavelength lying in the region of 1.6 .mu.m.
The converters of the second type mentioned, based on a thermal principle, essentially comprise a radiator which, when exposed to solar radiation, becomes red hot and emits radiation towards the photovoltaic cell, preferably with an emission peak matched to that of maximum sensitivity exhibited by the photovoltaic cell itself.
The above-mentioned converters have a number of disadvantages. In particular, for filter-type converters, heating of the cells occurs caused by background noise, i.e. by radiation not properly discriminated by the filters. Furthermore, there is unsatisfactory utilization of the band portion of electromagnetic radiation emitted by the sun and lying between 1.7 .mu.m and .infin., and in the case where it is desired to utilize also the radiation within this band, it is necessary to provide further filters and corresponding specifically designed photovoltaic cells, with a consequent increased cost of production which, however, is not based on a corresponding increase in the efficiency of the converter.
The converters of the second type also undergo heating caused by background noise and damaging to the radiator itself. Moreover, the peak emission of the radiator is relatively low and narrow in relation to the total spectrum of solar electromagnetric radiation, in which case the associated photovoltaic cell converts a reduced percentage of the solar energy arriving at aforesaid radiator.